This invention relates to a push-button switch device, and more particularly to a push-button switch device of the individual/interlocking action type wherein, when, for example, a first one of two buttons or keys is depressed, it is locked at its depressed position (individual action), and when a second one of the buttons is depressed with the first button locked at the depressed position, the second button is locked at its depressed position while at the same time the first button is released from its locked position (interlocking action).
Such a push-button switch device of the individual/interlocking action type is disclosed, for example, in Japanese Patent Laid-Open No. 61-47027. The push-button switch device disclosed is shown in FIGS. 6 to 17a and 17b wherein FIG. 6 is a fragmentary perspective view of the individual/interlocking action push-button switch device, FIG. 7 a transverse sectional view of the individual/interlocking action push-button switch device of FIG. 6, FIG. 8 is a detailed view of a stopper pin and its associated parts, FIG. 9 a longitudinal sectional view of the push-button switch device of FIG. 6, FIG. 10 a detail view of an interlocking plate and its associated parts of the push-button switch device of FIG. 6, FIGS. 11 to 16 are detailed view of the stopper pin and the interlocking plate of the push-button switch device of FIG. 6, and FIGS. 17(a) and 17(b) are a sectional view and a front elevational view, respectively, showing details of a heart-shaped cam groove of the interlocking plate of FIG. 10.
Referring first to FIGS. 6 to 10, the push-button switch device shown includes a casing 31 having a plurality of fixed terminals 32 implanted thereon, and a pair of operating members 33a and 33b each mounted for sliding movement in the casing 31 to control a movable contact 34 and having a sectoral hole 35 formed in a side wall thereof. A pair of stopper pins 36a and 36b are received in the sectoral holes 35a of the operating members 33a and 33b for rocking motion in directions of arrow marks J in FIG. 8 each around a fulcrum 37 provided by an end thereof. A pair of springs 38a and 38b are provided for returning the operating members 33a and 33b to their inoperative positions, respectively. An interlocking plate 39 is accommodated in receiving recesses 42 of the casing 31 and mounted for pivotal motion around an axis of a pair of support shaft 43 at opposite ends thereof. The interlocking member 39 has a pair of heart-shaped cam grooves 40a and 40b formed therein for engagement with movable ends 41 of the stopper pins 36a and 36b, respectively. A torsion coil spring 44 is provided for urging the interlocking plate 39 to resiliently contact bottom faces 45a and 45b of the heart-shaped cam grooves 40a and 40b of the interlocking plate 39 with the movable ends 41a and 41b of the stopper pins 36a and 36b, respectively. The torsion coil spring 44 has an operating end 46 thereof received in an operating groove 47 of the interlocking plate 39 and has a fixed end 48 thereof received in a fixing hole 49 of the casing 31. A cover 50 is provided for guiding the operating members 33a and 33b and for preventing operating members 33a and 33b and the interlocking plate 39 from being let off the casing 31 and is secured to the casing 31 by means of a pair of projections 51 formed on the casing 31.
Now, operating of the interlocking push-button switch device having such a construction as described above will be described.
At first, an interlocking action will be described with reference to FIGS. 10 to 17 wherein FIG. 10 shows the push-button switch device in a condition wherein one switch unit K is in a released condition while the other switch unit L is in a locked condition, and FIGS. 11 to 13 are sectional views of the heart-shaped cam groove 40a of the switch unit K while FIGS. 14 to 16 show sectional views of the heart-shaped cam groove 40b of the switch unit L. If a depressing operation is effected for the switch unit K in the condition shown in FIG. 10, the movable end 41a of the stopper pin 36a for the switch unit K will trace the heart-shaped cam groove 40a in a direction indicated by an arrow mark from a point M in FIG. 17. Thus, after the movable end 41a of the stopper pin 36a comes to a face N of the heart-shaped cam groove 40a of the interlocking member 39, the interlocking plate 39 is pivoted around the axis of the support shafts 43 as seen in FIG. 12 through the engagement between the movable end 41a of the stopper pin 36a and the face N of the interlocking member 39. As the interlocking member 39 is pivoted, the movable end 41b of the stopper pin 36b for the other switch unit L is disengaged from a point Q of the heart-shaped cam groove 40b as shown in FIG. 15 to allow the switch unit L to be changed over from the locked condition of FIG. 14 to its released condition shown in FIG. 16, thereby completing a releasing action of the switch unit L. As the depressing operation of the switch unit K proceeds further, the movable end 41a of the stopper pin 36a will finally reach a full stroke point P. If the depressing force is removed in this condition, the switch unit K starts its releasing action, and at the point Q of the movable end 41a of the stopper pin 36a with respect to the heart-shaped cam groove 40a of the interlocking plate 39, the switch unit K is put into its locked condition, thereby completing an interlocking operation of the switch units K and L. It is to be noted that a similar interlocking action occurs where the switch units K and L are in the respective reverse conditions. Now, a self locking operation will be described with reference to FIGS. 10 to 13 and 17. FIG. 10 shows the switch unit K in its released condition, and FIG. 11 shows a condition of the heart-shaped cam groove 40a in section when the switch unit K is in its released condition. It is to be noted that in this condition the movable end 41a of the stopper pin 36a of the switch unit K is positioned at the point M in FIG. 17. If a depressing operation is effected for the switch unit K in this condition, the movable end 41a of the stopper pin 36a will trace the heart-shaped cam groove 40a in the direction of the arrow mark until it passes a point N and reaches the full stroke point P. If the depressing force is removed in this condition, then the movable end 41a will trace in the direction of the arrow mark until it comes to the point Q at which the switch unit K is put into its locked condition. Here, if another depressing operation of the switch unit K is effected, the movable end 41a of the stopper pin 36a will trace in the direction of the arrow mark until another full stroke point R is reached. If the depressing force is removed here, then the movable end 41a will trace in the direction of the arrow mark until it returns to the point M whereupon the switch unit K restores its initial released condition. It is to be noted that a similar self locking operation occurs at the other switch unit L.
With such a conventional switch device as described above, since the two heart-shaped cam grooves 40a and 40b are formed in a predetermined spaced relationship in the interlocking plate 39, the distance between the operating members 33a and 33b which operate in association with the cam grooves 40a and 40b, respectively, is restricted of itself, and accordingly the switch device is low in versatility. Further, since the interlocking plate 39 is urged at a location displaced from the center thereof toward the movable ends 41a and 41b of the stopper pins 36a and 36b by the torsion coil spring 44 which is received at the operating end 46 thereof by the operating groove 47 of the interlocking plate 39 and at the fixed end 48 thereof by the fixing hole 49 of the casing 31, the urging forces acting upon the movable ends 41a and 41b are mutually associated with each other, and accordingly there is the possibility that the urging forces may not be balanced with each other. If good balancing therebetween actually fails, there is the possibility that the push lock mechanism may cause a malfunction.